Capacitive electronic discs (CED) have been developed which can have a relatively large volume of information. The recorded information can be, for example, various types of computer programs, large volumes of data, the text of books, manuals, catalogs and the like and electronic signal information. An advantage of CED's is that the volume of information which can be stored on a given size disc is many times greater than that which can be stored on conventional storage media such as magnetic tape, magnetic disc, audio type record or the like. A still further advantage of CED's is that if a sufficient number of copies of a given CED are molded the cost per disc is substantially less, on a volume of information recorded basis, than conventional recorded media such as magnetic tapes.
Video discs, a specialized form of capacitive electronic discs and video disc players have been developed for use with television receivers of the type normally used in the home. In U.S. Pat. No. 3,842,194 issued on Oct. 15, 1974 to Jon K. Clemens entitled "INFORMATION RECORDS AND RECORDING/PLAYBACK SYSTEMS THEREFOR" there is disclosed a video disc system which employs a video disc made of an electrically conductive material which is played with a video disc player having an electrically conductive pickup stylus. When the video disc is played, the stylus rides in a groove on the surface of the video disc and a capacitance is established between the stylus and the disc. The capacitance varies according to the geometric variations in the depths of the recorded signal in the bottom of the groove. The generated signal of varying capacitance is converted by electronic means into a plurality of electronic signals required to reproduce the recorded television program.
Capacitive electronic discs, such as video discs of the type disclosed by Clemens, can have an overall physical appearance similar to a conventional long-playing audio record. The CED is however, substantially different in kind from conventional audio records particularly with regard to the relative size of the recorded signal elements and the relative density of the recorded information. CED's have information molded into the disc in a geometrical configuration which in comparison to conventional audio records is at least on the order of a magnitude smaller. Conventional audio records are typically designed to operate at frequencies of about 10,000 hertz while being played at about 331/3 revolutions per minute (rmp). In comparison, CED's such as a video disc are designed to operate at frequencies of about 900 megahertz while being played at about 450 rpm's or even higher. The signal elements of a conventional audio record have a wavelength of about 6 microns. The signal elements of a CED have a wavelength on the order of 500 to 1,000 angstroms. The grooves on a conventional audio record are typically 50 to 60 microns wide with typically, substantially less than 200 grooves per centimeter. The groove width of a CED is only about 2.7 microns, and there are approximately 4,000 grooves per centimeter.
In the manufacturing process employed for the production of the CED's, most of the problems normally encountered in the manufacture of conventional audio records are encountered except that the problems are generally exaggerated because of the reduction in the size of the recorded elements.
The first step in the manufacture of records is to cut the initial recording into a substrate which then can be replicated to provide masters, molds, and finally the stampers which are used in the molding of the records. In the conventional prior art methods for the manufacture of audio records the information is recorded into a wax or, more preferably, a lacquer substrate. The recorded wax or lacquer substrate is then coated with silver or nickel. After a sufficient amount of the metal has built up, the recorded substrate is separated from the metal replica. Because of the relatively large size of the signal elements, the low density of the recorded information and the differences between the materials of the substrate and master, no substantial problems are encountered in separating the recorded lacquer or wax substrate from the electroplated metal master in the manufacture of audio records.
It has been found that the CED's cannot be satisfactorily recorded using wax or lacquer substrates, as the required minute details in the recorded grooves of CED's cannot be accurately cut and maintained in wax or lacquer substrates. The recording for a CED has to be made in an extremely hard fine grained substrate. The preferred substrate for the manufacture of a CED is an electro-deposited layer of fine grained bright copper.
After recording, the copper substrate is electroplated in the matrixing process to produce masters from which molds and then stampers are produced. It is extremely important to protect the recorded surface of the copper substrate from damage during the matrixing process, as any damage causes an undesired signal called noise which is repeated in each generation in the matrixing process and ultimately in the final molded CED's.
The most critical step in the matrixing process of CED's occurs when the copper substrate is electroplated with nickel to form a master. The electro-deposited nickel on the copper substrate must conform to the recorded surface of the copper substrate but, after the copper substrate has been electroplated with a sufficient amount of nickel to provide a self-supporting master, the resulting nickel master must cleanly separate from the copper substrate. If any of the nickel remains on the copper substrate or if any of the copper transfers to the nickel master, there is a deterioration of the desired signal and a corresponding increase in noise in the final CED.
To facilitate the separation of the electroplated nickel master from the copper substrate the surface of the substrate is passivated prior to electroplating. Passivation provides a protective coating layer on the recorded substrate which assists in the separation of the electroplated layer, that is, the master from the copper substrate.
Various methods have been suggested in the prior art for passivating metal surfaces such as for example nickel or noble metal surfaces. The most commonly employed method for passivating metal surfaces in the prior art is to initially wash the metal surface with an organic solvent, then with an alkaline cleaner mixture, then with a strong acid, and finally with a strong oxidizing agent.
The above method of passifying metal surfaces is widely used in the audio record industry. Ruggieri, U.S. Pat. No. 2,530,842 for example, discloses cutting the desired recording into a lacquer or wax substrate. The recorded lacquer or wax substrate, which does not require passivation, is then plated with a metal such as gold or silver to provide a master of the recorded substrate. The master is separated from the lacquer or wax cutting and the surface of the master is passivated as noted above, that is, by treating it with an alkaline cleaner, then with a strong acid solution, and then with a strong oxidizing solution.
The prior art three-step passivation procedure, that is, the alkaline treatment, acid treatment, and oxidizing treatment, while satisfactory for audio records, is unsuitable for passivating recorded copper substrates of the type employed in the manufacture of CED's. The multi-step passivation treatment appears to result in considerable damage to the surface of the recorded copper substrate. The damage to the recorded copper substrate is reflected as an undesirable increase in noise and causes reduction in the number of masters which can be satisfactorily formed from the recorded substrate.
It would be highly advantageous if a method could be provided for passivating the recorded copper substrates which would not adversely affect the signal-to-noise ratio and would permit an increased number of replicas to be made from a recorded substrate.